Add the ability to pass use flags through cbuildbot to build_packages.

Change-Id: I0e069217dd57c0c5f916da7152f3674849ce8469

BUG=http://code.google.com/p/chromium/issues/detail?id=78345
TEST=manual: a -full ( nousepkg ), a -bin (no extra), a useflag single, and a useflag multiple.

Review URL: http://codereview.chromium.org/6773013
2 files changed